The present invention relates in general to gasket configurations and in particular to multi-layer or composite gaskets of expanded graphite and aluminum which are mechanically secured together.
Starting from the general definition of a gasket as being a conformable, replaceable member for sealing areas and passageways between two juxtaposed members, the configuration and fabrication of gaskets has become increasingly complex and application specific. The once nearly ubiquitous cork gasket has been replaced by sophisticated, multi-layered products designed for specific applications.
One of the significant operating parameters that has prompted this change, at least within the automotive and vehicle field, is the increased operating temperatures of internal combustion engines in this service. No other single operating parameter so deleteriously affects performance and extended service life to the extent elevated operating temperature does.
Other difficulties are related to such elevated operating temperatures. They are the temperature cycling attendant each duty cycle of the engine and the dimensional expansion and contraction of the gasketed surfaces resulting from such operating temperature and temperature cycling. Another problem is the compression of the gasket which may change due to different temperature coefficients of expansion between the materials of the gasket, the gasketed member and the associated fasteners. Depending upon the composition of these components, increasing temperature may increase the compression of the gasket which, if it does not properly recover will be loose and perhaps leak at lower temperatures. This problem can, of course, occur in reverse, resulting in leakage at elevated temperatures. Ideally, a gasket will be sufficiently resilient to maintain its seal in spite of such temperature/compression cycling.
One commonly utilized gasket material has been steel. Such a gasket was effective in many applications but, as an increasing number of engine components become fabricated of other materials, the thermal coefficient of expansion differential often results in unsatisfactory gasket performance.
Another commonly used gasket material is graphite. Frequently, it is utilized in an expanded form with internal supporting matrices of other materials to provide suitable strength or it may be impregnated or mixed with other materials, again to provide suitable strength and durability, especially prior to installation.
One gasket application that has proven especially difficult relates to throttle body fuel injection housings. They operate at elevated temperatures, which rise to peak temperatures several minutes after shutdown, prepare and provide a fuel/air mixture deleterious to many gasket materials, and must be gasketed to the engine intake manifold.
A review of currently available gasket configurations reveals that improvements in both fabrication techniques and product performance are both desirable and possible.